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Final Exam Study Guide - GEOL 305
Terms in this set (49)
The different groups within the Theropoda and their relationship to each other
- non-avian therapods found on every continent, including antarctica
- most all became extinct by the end of the Cretaceous
- a well-diagnosed monophylethic group with many shared characteristics within the Saurichia group
The derived characters which are shared by all Theropoda
- clawed bipeds (obligate bipedals - unable to walk on front arms)
- many had serrated teeth (others none at all)
- all have/had hollow vertebrae and limb bones
range in size from < 1m (Microraptor) to animals growing up to 15 m in length (Tyrannosaurus, Carcharodontosaurus, Gigantosaurus)
- main functions of all forms were tracking, attacking, and feeding (but there was a lot of variety)
- Body was balanced directly over the pelvis, and the vertebral column held nearly horizontal
- hind legs were held close to the body, feet so close to the midline that one foot almost appears to be placed directly in front of the other (with digitrade stance)
The the range of form within the Theropoda for many skeletal characteristics and their use, including arms and hands, feet, legs and running ability, skulls, and teeth
-small-to-medium size theropods (Ornithomimosaurs especially), were most definitely fast runners (thigh bones are short compared to the length of the rest of the hind limb)
- the fastest theropods clocked at 40-60 km/h
- Reconstructed muscle mass and volume can also indicate speed of movement (this has been done for larger theropods) although they were still not the fastest
- evidence of swimming from a trackway in Spain ( the dinosaur swam with alternating movements of the two hind limbs, a pelvic paddle swimming motion - which is similar to those used by modern bipeds, including aquatic birds)
- dromaeosaurids and troodontids had especially sophisticated feet: the claw on digit II was huge, curved and sharp, and capable of a very large arc of motion (during normal walking and running it would have been held back or up, so as to protect it from damage) that claw would be brought forward as if spring-loaded and, with a powerful kicking motion of the leg, used to eviscerate the bellies of prey, perhaps disemboweling them in one stroke
- strong arms
- three-fingered hands (very dexterous) - the digits were long, capable of extreme extension, and tipped with powerful claws
- thumb (digit I) would fold across the palm in a semi-opposable way (could grasp and hold onto things)
- Maniraptorans had a specialized wristbone (a semi-lunate carpal) which allowed them to bend their hands at the wrist, back towards the bones of the arm
- large theropods such as Tyrannosaurus and Tarbosaurus, have very short arms (that can't reach their mouth), have bone structure in the arms that is stout and powerful, suggesting active use (suggested that the size of the skull of larger carnivores was so big that the upper limbs were reduced in size to balance out the weight. Larger front limbs would have made them too top/front heavy)
- the arms of Tyrannosaurus shows that the robust bones and large, stout claws at the tips of strong fingers could have lifted 300 kg, which is compelling evidence that they served some function.
- Skull: heads tend to be proportionately large, which is the case with carnivores in other animal groups as well.
The biggest head known in this group could be up to 1.75 m (5+ feet) in length
- the long and slender skulls as seen in Spinosaurus have a tendency to be rather primitive, looking not too different from the non-dinosaurian archosaur descendants
- more evolved have robust and deep-jawed skulls (ex - the powerful bite of the tyrannosaurids')
- Most of the theropods, even larger ones such as Carcharodontosaurus, had much more lightly built skulls than the Tyrannosaurids
- mechanics of defleshing can be compared to a falcon (slash and tear)
- tended to be flattened from side to side
- were recurved (curved backward)
- were pointed, and serrated
-The jaw joint in Theropods was at the level of the tooth row, so the jaws acted like scissors
- some had prominent serrations and narrow cross-sections, like hack-saw blades
- All ornithomimosaurs (except one primitive genus) lost all their teeth (small-skulled, long-legged, long-tailed theropods that look, somewhat, like ostriches, a beak with a ridged edge which is probably a shearing feature, skeletons have been preserved with gastroliths, so they no doubt relied on them to grind their food since their teeth wouldn't have done the job)
- Oviraptorosaurs were also toothless (skull was very short with pneumaticity (apparently), jaw musculature was very well developed, in the middle of the palate are a pair of stout, peg-like projections - used for crushing)
The current knowledge of Theropoda senses, center of balance, intelligence, presence/absence of feathers, diet, and nesting behavior
- Fossil Recovery: most cases they are isolated, individual skeletal remains, although there are rare instances of bone beds of a single theropod species
Senses: extremely important for a hunting lifestyle
- size of the olfactory bulb in Tyrannosaurus is huge (heightened sense of smell)
- Sharp vision was important for all theropods, and their eye size is large
- In Dromaeosaurids (including Deinonychus, and Velociraptor), and especially in the Troodontids, the eyes have migrated to a more forward position, giving overlapping fields of vision which would mean these animals saw stereoscopically
- narrow snouts of Tyrannosaurids allowed 55° of binocular vision, less than humans or owls, but still far more than hadrosaurs
-The middle ear cavities of both troodontids and ornithomimosaurs are greatly enlarged, such that they would have been very good at hearing low frequency sounds; in troodontids they would have been able to tell which direction the sound came from
- horizontal position of the vertebral column and the center of gravity being positioned near the hips gave theropods very good balance
- Deinonychus was aided by having its tail stiffened by elongate processes along the neural arches. It was flexible at its base only, directly behind the pelvis
- theropods = within bird range for intelligence (had more complex perceptual ability and more precise motor-sensory control than birds) This implies sophisticated inter- and intraspecific behavior
- theropods have been fossilized with remains in their stomachs of lizards, mammals, fish, and hadrosaur bones. Tyrannosaurus coprolites found have been 30-50% bones, including parts of a ceratopsian frill
- evidence of cannibalism from tooth marks (found on bones) as well as bones in the stomach of the same species of dinosaur
- seem to be social, gregarious animals
- horns or head crests in some therapods, which may have functioned, much as head ornamentation of hadrosaurs and ceratopsians, in social behavior/ritual display
- larger theropod skulls have slightly elevated upper margins on the snout, and/or raised and roughened bumps over the eyes ( believed to have been cores for hornlets (small horns) made of keratin) which could have also been used for head-butting (they are more developed in adults than in children)
- sexual dimorphism is found in two theropods, Syntarsus and Coelophysis (one morph has a long skull and neck, thick limbs, and powerfully developed muscles around the elbow and hip; the other form has a shorter skull and neck, and slender limbs. The larger, more robust form is thought to be the female)
-Brooding behavior is known in Oviraptorosaur, with adult skeletons found on top of nests of eggs with Oviraptorosaur embryos inside. A more recent find in Mongolia of this behavior was that of Gigantoraptor.
- a 10-15 fold increase in body size from hatchling stage to adult (growth is thought to be very rapid)
- probably k-strategists (cared for young)
The earliest forms of Theropoda
- Coelophysoidea, named after Coelophysis, and includes some related, less well known forms
- Ceratosauria, named after the Jurassic Ceratosaurus, and including some other big forms such as the Cretaceous Carnotaurus
- Tetanurae (means stiff tail)
basic facts about the dinosaur genus Tawa
-This dinosaur was first discovered when several bones were found exposed in 2004 by some hikers who had stumbled across them
- Tawa ranges in length from 2-4 m
- Tawa has a mix of features found in both Coelophysis and Herrerasaurus, and although it shouldn't be considered the "missing link" it does tell us about the progression in form between these two groups
basic characteristics of the Coelophysoidea
- All members of this clade are medium sized carnivores, 2-4 meters long, with long, slender bodies and, generally, slender skulls
- The best known of this clade is that which gives it its' name, Coelophysis
The collection locality and other basic facts about the dinosaur genus Dilophosaurus
- This genus is the largest of the dinosaurs in this clade
- double crest on the top of the head
- the hand has four digits (the fourth digit is vestigial, or reduced), and the foot has three digits (fourth and fifth extremely reduced)
- The premaxilla (at the tip of the snout) is loosely attached to the maxilla (to the left of the premaxilla; it is the primary tooth-bearing bone of the upper jaw). This is a diagnostic characteristic of most ceratosaurs
- a fairly large ceratosaur; about six meters (20 feet) long, and quite slender
- about 150 myo
The timing, variety, and general characteristics of dinosaurs in the Ceratosauria
- started out in minor numbers in the Early Jurassic, but by the Late Cretaceous, were dominant in a large part of the terrestrial ecosystems, particularly in the southern hemisphere and Europe
- reduction in the number of fingers, and strength, of the hands
- a variety of forms, including the toothless, and probably herbivorous, Chinese Limusaurus of the early Late Jurassic, and the Late Jurassic Elaphrosaurus. Along with several other genera these two are usually put into an "unofficial" group: the Elaphrosaurs
- toothed members of this group wouldn't have been able to bite and hold on to their prey, so would probably depended on cutting, or biting chunks out of their prey, weakening them by blood loss to their eventual death
- Neoceratosaurs have shorter and thicker necks than the primitive forms (two major groups within this clade, the Ceratosauridae and the Abelisauroidea)
- typified by Ceratosaurus, from the Late Jurassic of North America. This genus has members which vary from 6-8 meters in length
- Abelisauroidea: within are two clades, the Abelisauridae and the Noasauridae (tend to have elongated prongs on their vertebrae. The Noasauridae are smaller and slender, typified by Noasaurus from the Late Cretaceous of Argentina) also includes the Majungasaurus from Madagascar. This group is typified by tiny arms, which in some members couldn't even bend at the elbow as the ulna and radius were reduced to the size of wrist bones (carpels). Their legs were usually shorter, and stockier, than in other Ceratosauria.
- The Abelisaurids had a tendency to have a lot of horny, (keratin sheathed?) texture on their skull (as seen in Majungasaurus) and their snouts had a tendency to be shorter, and rounded, with short, thickened teeth.
- The Abelisauridae were the top predators of the Late Cretaceous on the land masses of India, Madagascar, South America, and Europe. Larger, later forms haven't been found on Australia, Antarctica, or continental Africa, at least not yet
Two key characteristics of the clade Tetanurae given herein
1. the back ½ of the tail is stiffened by interlocking zygapophyses (used as counterbalance) The tail is most flexible where it meets the body, and the flexibility of the tail decreases through the evolution of the group to more recent forms
2. developed true pneumaticity, with extensive air sacs, and highly efficient unidirectional breathing, such as we see in modern birds
The major groups which comprise the Tetanurae
- Basal Forms: the Early Jurassic Sinosaurus (China), and Cryolophosaurus (Antarctica)
85 million year old Aerosteon, a basal tetanuran discovered in 1996 in Argentina
- More advanced but still of Medium build: Monolophosaurus, Middle Jurassic, Shishugou Formation, in Xinjiang, China
-MORE DERIVED TETANURAE WITHIN THE ORIONIDES (HUNTERS) ARE THE SPINOSAUROIDEA, CARNOSAURIA, THE COELUROSAURIA
- More derived = Spinosauroidea: including Megalosaurus, one of the first dinosaurs ever found, and its' close relation Torvosaurus, somewhat related Afrovenator and Piatnitzkysaurus, and the less closely related Spinosaurus and Baronyx, plus some others ( Late Jurassic to mid-Late Cretaceous dinosaurs of large proportions, elongate snouts, and in some, tall dorsal neural spines which were probably covered in a skin membrane - some also had an enlarged thumb claw and aquatic diet) also within this group are Baronyx (Early Cretaceous, Europe), Irritator (Early Cretaceous, Brazil), Ichthyovenator (Early Cretaceous, Thailand), and Spinosaurus (early-Late Cretaceous of North Africa). Suchomimus (Early Cretaceous, Northern Africa) is thought by some to possibly be a species of Baronyx
- WITHIN THE ORIONIDES, THE CARNOSAURIA AND THE COELUROSAURIA COMPRISE THE CLADE AVETHEROPODA (These groups share the loss of digit IV, causing the hands to have 3 digits, matching the number of toes)
The type of body forms found within the Spinosauridae and the Carnosauria
- Spinosaurids are Late Jurassic to mid-Late Cretaceous dinosaurs of large proportions, elongate snouts, and in some, tall dorsal neural spines which were probably covered in a skin membrane. (Some Spinosaurids and Megalosaurids also had an enlarged thumb claw)
-Carnosauria: the loss of digit IV, causing the hands to have 3 digits, matching the number of toes. The Carnosauria of the Cretaceous are almost all Carcharodontosaurids. The more advanced forms are generally larger with proportionately larger heads and reduced digits of the hand.
The name, timing, and characteristics of the dinosaurs which are basal members of the Coelurosauria
Overall, the Coelurosauria clad includes:
- large theropoda such as the Tyrannosaurids
- small forms, as well as the Maniraptora (such as Ornithomimosaurs, Oviraptorosaurs, & Therizinosauroids)
- non-avian theropods closest to birds: Avetheropoda: Eumaniraptora
The basal forms of the Coelurosauria belong to family Compsognathidae. These dinosaurs are slender, with long, narrow hands and feet
Within this family are Compsognathus, of the Late Jurassic of Europe, and several genera from the Early Cretaceous of China, including Sinosauropteryx, and the unusually long, for this clade, Sinocalliopteryx, which measures in at 2.5 m in length.
The advanced characters given for each clade within the Tyrannosauroidea and have an understanding of the variety of body form for the group through time
Through the Cretaceous, tyrannosauroids increase in size. A typical mid-size form is Appalachiosaurus of the Late Cretaceous of North America.
- They shared multiple advanced characters, including a proportionately large skull with a deepened jaw which had extremely deep rooted teeth, and a complete loss of the hand digit III.
- There are slender forms, and those with more slender skulls. Most are heavily built. All relied on their jaw strength for killing their prey. The largest of these were probably not as fast as adults as they would have been at a younger age.
What is meant by the concept Convergent Evolution, and how that concept is manifested within the Theropoda
They may have come from dissimilar ancestors, but they have evolved features to adapt to a certain predatory lifestyle.
- proportionally large heads
- a tendency towards shorter arms
The changing view of the relationship between large skulls and reduced front limbs within the Theropoda
- Before 2009, it was thought to be AN ADAPTATION FOR GETTING BIG (In order to maintain agility, with the increase in head size, the front of the body itself had to get smaller, thus the evolutionary push towards stunted arms)
- With the discovery of Raptorex, however, that idea was put to question. Raptorex has the body style like that of a much larger carnivore, but it is much smaller.
Raptorex is much older, being found in deposits which are 125 million years old, at the very beginnings of Tyrannosauroid evolution. T. rex itself is one of the last Tyrannosaurids to live, known from the Late Cretaceous only.
General facts and characteristics of the Maniraptoriformes
- Maniraptoriformes as a group have a smaller skull and a reduction in the tooth size compared to the larger genera of the Tetanurae. These changes point towards possibly omnivory (eating a mix of plants, animals, insects, etc., and even possibly full herbivory.
- range from Late Jurassic, to the Late Late Cretaceous in age
- known from every continent except Antarctica, and that may well be just because most of the continent is covered by ice, and the collecting season there is incredibly short
- Many specimens of this group have been found with feathers (broad and pennaceous, meaning with a shaft, and several sets of branching)
- True pneumaticity of the bones, with extensive air sacs, and highly efficient unidirectional breathing, such as we see in modern birds. These adaptations increased in complexity through the evolution of the Maniraptora and Aves, so it is felt that highly derived Theropods probably would have had such an efficient method of breathing that they could have sustained high levels of activity
- Key feature is that the back ½ of the tail is stiffened by interlocking zygapophyses. The tail is most flexible where it meets the body, and the flexibility of the tail decreases through the evolution of the group to more recent forms
(Within the Maniraptoriformes are the Ornithomimosauria and the Maniraptora clade, which itself includes Alvarezsauria, Therizinosauria &, Oviraptorosauria, and the Eumaniraptora)
The characteristic features of all Ornithomimosaurs
- a group of small to medium size Coelurosauria, usually lightly built
- smaller heads, and reduced or absent teeth
- eyes are large, and they probably had at least some degree of stereoscopic vision
- Neck, arm & hand, and leg are all long and slender
- toes were short and clawed
- Some specimens have been preserved with gastroliths
- the pennaceous feathers are known only on the arms
The variety of forms within the Ornithomimosaurs
- Most Ornithomimosaurs lived in areas with an ample amount of water, including river estuaries, lake valleys, and well-watered forests. Their diet (depending on species and habitat) varied from plants, to smaller aquatic organisms, including fish
- Less advanced genera include small to large Ornithomimosaurs which have been found in Africa, and include the Early Cretaceous 1.6 m long, 10 kg, Shenzhousaurus orientalis, from NE China, and the unusually large later Cretaceous Deinocheirus mirficus
The collection history and gathering of knowledge about the Ornithomimosaur Deinocherirus
-discovered in 1965 in the Nemegt region of Mongolia
- a collection of (most of) the front limbs, each of which was 8 2.4 m long(!), plus some of the claws, and bits of ribs and vertebrae
- Recently (2006 and 2009), material was found at different quarries in the same region, and a more complete picture of this species can be formed (although that newer material was missing the skulls, hands, & feet) making it one of the tallest theropod dinosaurs ever found - also found that it was a sail-back dinosaur
- skull was hypothetically poached from Mongolia and sold to a museum in Europe
General facts and characteristics of the Maniraptora
- adapted the wrist with many of the clade having the development of a semi-lunate carpal, a wrist bone modification that increased manual dexterity and the ability to sever flesh from the bone of prey
- include small to gigantic predatory and herbivorous coelurosaurs of the Late Jurassic to the end of the Cretaceous
- highly variable in presence/absence of teeth, size of the head, length of the arms, length of neck and tail, and number of fingers on the hand (1 - 3). They do all share the character of an enlarged brain
Characteristic features for each of the clades: Composgnathids; Alvarezsaurids; Therizinosaurs; Oviraptorosaurs.
- Composgnathids: small predatory maniraptors known from localities in Eurasia and South America which are Late Jurassic to Early Cretaceous in age. Their neck & legs are long, and the tail especially so. The thumb and first finger of the 3 fingered hand were stout and strong. Their skulls were very light due to the enlarged eye orbit and skull fenestrae
(could find pigment color thanks to fossilized melanosomes - pigment bearing organelles)
- Alvarezsaurids: ranges in age from the Late Jurassic to the end of the dinosaur era. Had unusual skeletal characteristics: teeth were small, numerous, stout and semi-tubular. Arms were very short but very powerfully muscled (the hand made of one, massive funtional finger with large claw - function not understood but possibly used for tearing apart termite mounds). The public bone of the pelvis is retroverted (pointing backwards like Ornithischians).
- Therizinosaurs: range in size from small to large, and lived during the Cretaceous in the Northern Hemisphere. They are thought by many to be herbivores, unusual for a theropod. These are highly evolved mantiraptoran theropods, and the larger and more heavily built species have been compared to giant ground sloths. They had small heads and long necks, but unlike them the Therizinosauria had extremely elongated and powerful claws on their front limbs. Large guts, Short legs, long necks and beaks, and built their nests in colonies to protect from predators.
- Oviraptorosaurs: Small to large, flying (according to some analyses) and flightless herbivorous or omnivorous maniraptorans, of Cretaceous age; known only from the Northern Hemisphere. The head is not large compared to the body size, and the skulls are typically short and deep. Teeth are reduced or absent. Neck is proportionately long. Tail is short. Both arms and legs vary in length in the different genera within this clade from long to short; arms have two or three fingers.
(NOTE) Recognize members of each of the clades mentioned above when presented with pictures of fossils, or whole body reconstructions
the skeletal characteristics of the Deinonychosauria & have an general understanding of the lifestyles, sensory perception, and social behavior of the Deinonychosauria.
- highly predaceous and intelligent carnivores
-sickle-clawed troodontids and dromaeosaurids
- Clawed bipeds with hollow bones
- Appear early on in dinosaur evolution
- Most Mesozoic forms
had grasping, three-fingered hands with a semi-opposable thumb
had recurved, serrated, laterally compressed teeth
and were carnivores
- developed eviscerating claws on the leg
- had grasping, powerful hands
- Through the evolution of the clade, the proportional length of the limbs to the body size changes (due to style of hunting - ex: persuit vs ambush predator)
- had large brains to body size (and inferred higher intelligence)
- large eyes, and likely, stereoscopic vision
- were pound for pound the deadliest carnivores that evolved in Dinosauria, and they are the group most closely related to birds (Avialae)
- very active = probably endothermic
diagnostic features of living birds.
- Flight- asymmetrical with interlocking barbules on vanes
- Contour- symmetrical, shorter than flight, with downy lower part
- Down- no shaft; fluffy vanes
Loss of teeth
Large brains and advanced sight
Carpometacarpus- the wrist and hand bones of modern birds are fused into a unique structure which is composed of three fused fingers, thought to be digits I, II, and III.
Legs and Feet - fully bipedal, with an erect stance
Twin shin bones (tibia and fibula) are unequal: the tibia is large, the fibula very slender and thins towards the ankle.
Feet are clawed and have 3 toes in front (digits II, III, & IV), and smaller toe (digit I) at the back.
The 3 central metatarsals (foot bones to which the toes attach) are fused together with some ankle bones into a unique structure called a tarsometatarsus.
Pygostyle. No living bird has a long tail. The bones in most cases are in a compact, vestigial structure of fused bones.
Pneumatic bones. Living birds breathe unidirectionally with a complex system of air sacs.
Rigid skeleton- light and rigid to provide a platform to which the wings and muscles that power them can attach.
In the shoulder, pillar-like coracoids bones buttress against the front of the sternum, the scapula, and against paired, fused collarbones called the furcula (we know this as a wishbone). This set-up is unique to birds.
the collection locality for all specimens of Archaeopteryx, and its skeletal characteristics.
Late Jurassic formation in Southern Germany (Bavaria). It was found in the mid 1800's and its mixed reptillian and bird characteristics made it a huge mystery. It had feathers but also a long tail with hands and claws
Skull- typically archosaurian with blade-like, unserrated, recurved teeth
Arms and hands- arms are 70% length of the legs
Hands about as large as feet
Each hand has 3, fully moveable, separate fingers
Each finger tipped with a recurved claw
Wrist bears a semi-lunate carpal
Legs and feet- Foot has three toes in front, and a fourth toe lies to the side (or behind)
3 in front ~ symmetrical around digit III
All toes have well-developed claws
Ankle has a modified mesotarsal joint. 3 foot bones are unfused. Thighs shorter than shins; fibula splinter-like as it approaches the ankle.
Long bones are thin with hollow spaces
Trunk and tail
Primitive, unfused archosaurian pelvis.
Long, straight, well-developed tail.
On the tail vertebrae, projections from the neural arches (zygapophyses) are elongate; tail must have had very little flexibility or possibility of movement along its length.
Feathers- These fossils have well-preserved impressions of feathers. Some of the best preservation is of the flight feathers.
the shared characters between Archaeopteryx and the larger clades starting with the Archosauria.
Archaeopoteryx exhibits diagnostic features of archosauria, and also the erect stance, and the modified ankle joint of a dinosaur.
It has hollow bones, a feature it and modern birds share with Theropods. It also has the enlarged 3 fingered hand that Theropods have.
Archaeopteryx has a furcular (wishbone), diagnostic of Tetanurans, and also has the elongate zygaphophyses which would have stiffened its tail.
It possesses the distinctive semi-lunate carpal, a shortened ischium, and large, circular orbits, diagnostic characters of the Coelurosaurs.
Archaeopteryx has a grasping, 3 fingered hand, like the maniraptorans, along with an elongation of the middle digit.
It has a highly reduced fibula, and forelimbs that are equal to or greater than the length of the hindlimbs, diagnostic of the Eumaniraptorans.
As in all avialans, Archaeopteryx has tail vertebrae which show an extensive elongation of the hemal and neural arches, and the teeth in their skull have lost their serrations.
CONNECTIONS TO THERAPODA:
Although the fingers in birds are fused, they are recognized as being the same three which are prevalent in the hands of Theropoda.
Pneumatic bones are hollow, and it would be easy to think that they evolved as an adaptation for lightness.
Pneumatic bones are present in several lineages of Saurischians, including the large sauropods with the pleurocoels in their vertebrae.
Obviously the sauropods couldn't fly, so pneumatic bones didn't evolve specifically for flight in birds as they were present in organisms long before the first actual bird appeared.
feathers; their structure, theorized evolutionary beginnings, and purpose.
- Display function (sexual selection)
Old fashioned thought is that feathers evolved from reptilian scales, but more recent work points to a different origination point. It is thought that feather formation is due to the interaction of specialized follicles, and a series of specialized genes that control the onset and termination of growth.
Four sequential stages of feather evolution have been identified:
1. Formation of a hollow cylinder (the shaft)
2. Loosely associated, unconnected, unhooked barbs (downy feathers)
3. Hooked barbs on a symmetrical vane (contour feathers, such as wrap around the body)
4. Hooked barbs on an asymmetrical vane (flight feathers)
several of the recent dinosaurian finds which have feathers and understand the connections between living birds and theropod dinosaurs.
- Anchiornis is a small feathered eumaniraptoran dinosaur from a Late Jurassic (~155 my) age locality in Liaoning Province.
(We know the colors of the feathers in Anchiornis because of the preservation of the melanosomes within the feathers.)
- There is also a 124myo locality in Liaoning Province, China which has excellent preservation of generally complete and completely articulated animals. The fine mudstones show the impressions of the animals' coverings and also some dark staining, probably the original organic matter.
The first discovered organism from that locality is Sinosauropteryx, a small coelurosaur which did not have the proper skeletal design to be able to fly. It was covered in barb-like filaments.
- Also at that locality was the somewhat larger, toothless Caudipteryx, an oviraptosaur.
There was a very large, ostrich-sized, therizinosaurid named Beipiaosaurus, which also would not have been able to fly. This animal has primitive feathers with only barbules.
The elongated, single filament feathers of Beipiaosaurus are very apparent on the photo of the fossil.
Sinornithosaurus, a non-flying deinonychosaur, had feathers that in every way are comparable to those of modern birds.
The development of feathers coincides with the development of tetanuran dinosaurs.
More basal tetanurans, such as the coelurosaurs have basal types of feathers. More derived tetanurans, like the eumaniraptorans, bear more derived feathers.
We also have evidence of the connection between theropods and birds through studies of soft tissue.
In 2006, organic soft tissue was obtained from a Tyrannosaurus femur. The molecular composition of one of the proteins therein, collagen, more closely matched those of a living chicken than any other living animal.
prevalent theories for the development of flight.
- Arboreal- That bird flight originated by birds gliding down from trees. Gliding would be a precursor to flapping. Perhaps flapping began as modifications of motions used to control the direction of gliding.
-Cursorial- That bird flight originated by an ancestral bird running along the ground. Perhaps to avoid obstacles, the animal would leap and become temporarily airborne. In a bid to overcome the force of gravity, flapping flight would have developed early on.
well-known Mesozoic birds and some forms that are close, but perhaps not birds, such as Rahonavis.
- possessed the sickle-shaped claw and the long tail of a dromaeosaurid
- also had more sophisticated features, such as the pneumatic foramina, (openings into the pleurocoels which were necessary for unidirectional breathing)
- this type of breathing (a bird characteristic) infers a more efficient metabolism
forces which caused the progression of adaptations for flight proficiency & the prominent avialians in the Family Confuciusornithidae which exhibit those evolutionary changes.
- formation of a pygostyle (fused tail bones)
- development of the synsacrum (fused vertebrae and pelvis) and other features for a rigid trunk
After these early Cretaceous forms, the continuation towards birds led to
- a reduction in the number of trunk vertebrae
- an alteration of the shoulder joint
- fused digits of the hand into a carpometacarpus
the Enantiornithes, and know their derived & primitive characters.
- Arboreal (lived in trees)
- Well developed flight capabilities
- Most diverse clade of Mesozoic birds
- All went extinct before the close of the Mesozoic era
- Worldwide distribution, with forms found in Spain (Iberomesornis, early Cretaceous) Australia, China, Uzbekistan, Mexico, Argentina, and the USA.
These birds had a modification of the wrist joint that allowed them to fold their wings back tightly against their body, a new feature never before seen.
They also developed adaptations to allow perching: the first toe is positioned opposite of the others (as in modern birds).
Primitive features in this group include:
- Gastralia (belly ribs, a throwback to archosaurs)
- relatively numerous back vertebrae
- unfused tarsomatarsus
- unfused pelvis
the Ornithuromorpha, the lineage leading to Aves.
This group is represented by Vorona, in the late Cretaceous of Madagascar, and from the same time in Argentina, by Patagopteryx.
Also in this group are all the remaining birds in a clade known as Ornithurae.
There at least 15 unambiguous characters which unite all the members of the Ornithurae. The living Aves are in this group, as well as the Hesperornithiformes, and the Ichthyornithiformes, (both Cretaceous in age) the closest fossil relatives to living birds.
the Hesperornithiformes, their lifestyle & derived characters.
- monophyletic clade
- large, long-necked, & flightless
- teeth in their jaws
- greatly reduced arms
- diving birds which used their feet and powerful hind limbs for propulsion
- hind limbs oriented to the side of the creature, and could not be brought under the body
Because of the position of the hind limbs (which hindered walking on land), and other features, this group was well adapted for swimming in the ocean.
- long, flexible neck useful for catching fish (evidence from coprolites which had numerous fish skeletons preserved within)
- similar to modern loons and cormorants (diving birds) in that some of the pneumaticity in the bones was lost
- furcula, coracoids, and forelimbs highly reduced because strength for flight was no longer necessary.
- positioning of the hind limbs is to the sides, and they have greatly reduced fore limbs
the Ichthyornithiformes, their lifestyle & derived characters.
- a deep, keeled sternum, and an extremely large deltoid crest, both adaptations for powerful flight musculature
It shared many adaptations found in modern birds:
- shortened, fused trunk
- a carpometacarpus
- a pygostyle
- a completely fused tarsometatarsus
- a synsacrum formed of 10 or more fused vertebrae
-found only in marine deposits (lifestyle like a modern gull - except it had teeth)
the general steps in the evolution of Aves.
Organisms in this clade have as many as 11 unique characters of the skull, pelvis, and ankle.
Mesozoic fossils of this group are fragmentary, scattered, and rare, being found only in the late Cretaceous.
- Screamers and waterfowl (Anceriformes)
- Loons (Gaviiformes)
- shorebirds such as sandpipers, gulls and auks (Charadriiformes)
- Sage grouse, quail, pheasants, etc.
- wing-propelled divers such as modern petrels (Procellariiformes)
- Parrots (Psittaciformes)
EVOLUTION OF AVES:
1. Development of the perching adaptation in the foot, in combination with limited flapping flight capabilities
2. Development of a pygostyle
3. Reduction in number of trunk vertebrae; and development of a flexibule furcula, strut-like coracoids, carpometacarpus, and fully folding wings
4. Further reduction in the number of trunk vertebrae, loss of gastralia, final rotation of pubis to lie parallel with ilium and ischium (bird-hipped condition).
5. Reduction in number of trunk vertebrae, decrease in size of acetabulum (hip socket), patellar groove: a groove at the distal end of the femur to accommodate the patella (knee cap).
6. Finally, loss of teeth (in Aves)
Steps 1-5 occurred in the Mesozoic; step 6 may have occurred in the Cenozoic, because all Mesozoic avialans, for which a skull is known, had teeth.
Cladogram of the Eumaniraptora
Groups: Deinonychosauria and Avialae (Aves and non-avian very near relatives)
The different types of metabolisms and thermoregulation of dinosaurs
Endoderms: organisms which regulate their temperatures internally.
Ectoderms: organisms that use external sources of heat to regulate their temperatures, like lizards which lay in the sun.
Studies of the evidence in the fossil record of Dinosaur metabolisms show that there are probably no living vertebrates which have a metabolism that is a close match to the Dinosaurs
Thermoregulation: Anatomical evidence
- Stance- All non-avian dinosaurs had erect stance (all modern creatures with erect stances are endotherms - the controlled temperature is necessary for the musculature to remain in an erect stance)
- Buccal pumping (in organisms with sprawling stance because the weight shifts from one side to the other so only one lung can inflate at a time) vs using both lungs (more volume = better locomotion)
- Limb anatomy, inferred activity levels (longer strides = more efficient: higher levels of activity for a longer period of time before entering an anaerobic physical state), and calculated walking and running speeds (height to hip, stride length)
- Assorted adaptations for processing large volumes of food (secondary plate for chewing)
- Hearts: # of chambers = 4 (2 distinct circulatory systems: one for the lungs (pulmonary), and the second for the rest of the body (systemic circuit))
- Minds: Intelligence (higher in endotherms due to metabolism providing more neuromuscular control) Air movement and water loss (The lungs must be able to replenish the system with fresh air quickly for endothermy to be present. That would lead to water loss unless systems are in place to prevent it. Modern mammals have respiratory turbinates (conchae) in the nasal cavities, convoluted sheets of delicate tissue-covered bone. These moisture covered surfaces pull water out of the exhalant air before it exits our bodies) many dinosaurs have olfactory turbinates that would aid their sense of smell, but none are known to have respiratory turbinates
- Histology: Bone growth Timing of growth from egg to adult
Haversian bone is bone growth done by "remodeling" older bone (dissolution of primary bone and redeposition of secondary bone).
That secondary bone is redeposited in Haversian (vascular) canals (middle of nested cylinders), and resorption/redeposition can be done repeatedly during growth.
Eventually, dense, secondary Haversian bone is formed. That type of bone is found in birds and mammals.
Secondary Haversian canals are known to be correlated with:
-size and age, and even possibly with the type of bone being replaced
-the amount of mechanical stress undergone by the bone
-nutrient turnover (the metabolic interaction between developing bony tissue and soft tissue)
Bone growth was very rapid (more like birds than modern reptiles)
Thermoregulation: Ecology evidence of predators and prey
Need to go back
Thermoregulation: Zoogeography evidence
Dinosaur distribution compared to modern distribution for crocodiles and snakes
Need to go back
Thermoregulation evidence: Phylogeny
(Insulation and Geochemistry)
Need to go back
How paleontologists can use gathered data to infer the metabolisms of different types of dinosaurs
Need to go back
The scope of the extinction event in which Dinosaurs disappeared
- 16% of the families of marine organisms died out
- For both marine and terrestrial organisms, the estimates are that 75% of the species went extinct
- Shelled cephalopods groups survived (3 groups of Ammonites and one Nautiloids)
The evidence for a large scale volcanic eruption contemporaneous with the extinction
- involve the ejection of toxic gases, water vapor, and particulate matter into Earth's atmosphere
- it's ash (if a large amount) can block sunlight, and cool Earth's overall temperature by 1-2 degrees Celsius for several years
- close to the timing of the mass extinction an eruption of major flood basalts occurred in what is known as the Deccan Traps, exposed in SW India (caused by the subduction of the continent under Asia)
=> amount of lava that was erupted is estimated at 2.6 million km2, and all within a 100,000 to 200,000 year window right around 65 million years ago
- rapid release of CO2 during these eruptions would have overwhelmed the surficial systems and sinks, and triggered rapid greenhouse warming at the K-T transition
The evidence for a large bolide impact contemporaneous with the extinction
"bolide" = a large meteor that explodes in the atmosphere
- Some geologists feel that these flood basalts (and the hot spot) occurred due to an impact of an extraterrestrial body with the Earth at that geographic locality (evidence: the Shiva Crater in the ocean crust off the SW coast of India)
-Impacts (which would throw up enormous quantities of dust) could, in theory, cause global cooling by blocking out sunlight.
- several other (smaller) craters of around the same age as Chicxulub and the larger Shiva have been discovered, all between latitudes 20°N and 70°N. Examples include the Silverpit crater in the United Kingdom, and the Boltysh crater in Ukraine, both of which are much smaller than Chicxulub but likely to have been caused by objects many tens of meters across striking the earth ( could be explained by a much larger object which broke up into multiple parts upon contact with the earth's gravity well and atmosphere)
-In the mid-1970's, geologists investigating the K/T (Cretaceous/Tertiary) boundary in Italy discovered a spike in the amount of Iridium within the layer, many times what would normally be found. The element Iridium is found in large quantity in meteorites and can also be added to surface sediments by unusually high volcanic activity. When a bolide of major size hits Earth, a good portion of that object would be vaporized into dust upon impact, spreading the resulting dust high into the atmosphere and thus around the entire planet
-Shocked Quartz- When a large object "rings the earth's bell", quartz grains in rocks of the nearby region will develop parallel fractures due to the "shock" of the impact. Shocked quartz was found in rocks surrounding the Gulf of Mexico, especially to the northwest
- Tektites- Small globules of "frozen" rock (glass) that form when the heat of the incoming bolide vaporizes itself and part of the earth's crust are found in the sediments in proximity to the impact site. Tektites were found in sediments surrounding the Gulf of Mexico and strung out to the Northwest as far as Colorado
-Soot layer- Heat of impact starts massive wildfires in surrounding terrain, leaving behind a soot layer in the sediment. Anything that falls through the atmosphere will heat up due to the friction of its passage. A recent example of this occurred in early 2013 in Russia when a meteor (estimated at 20 meters in length) entered the atmosphere at a low angle of trajectory.
- Any such impact which occurred in the ocean would cause a major tsunami. There is evidence of tsunami waves on the shorelines surrounding the Gulf of Mexico
- 10 km meteoroid left a 100 km crater
- Some of the cenotes of the Yucatan position seem to line up along the "fracture" zone that developed around the perimeter of the crater. Mapping the gravity anomalies of the Yucatan also reveal differences in a bull's-eye pattern (Cenotes are deep holes in Limestone bedrock which form due to the dissolution of the bedrock by groundwater along fracture zones)
The consequences of these events to life on earth
- Addition of Carbon Dioxide (CO2) to the atmosphere from volcanic eruptions would cause acidification of the oceans
=> issues in air quality for terrestrial organisms (would have been more devastating for shallow water than deep, and for warmer-water organisms than those that lived closer to the poles)
- Particulate matter and ash from volcanic eruptions could block out the sun
=> stopping photosynthesis by plants in both the marine and terrestrial realms (entire food web will suffer)
- considerable evidence that the Angiosperm forests of the Late Cretaceous were replaced by ferns and other spore-bearing, more primitive vegetation (more successful in barren environments)
- ongoing environmental stressors due to climate change
Of other theories for the demise of the Dinosaurs
- a cooling of the earth would have started the demise of the dinosaurs long before the actual impact of bolides such as that which occurred at Chixulub. This cooling would have caused a change in the mix of plants available for the herbivorous dinosaurs
- a virus evolved to which the dinosaurs were particularly susceptible
- the dinosaur lineage had been active on Earth for so long that it was becoming senile
- the dinosaurs developed cataracts from being out in the sun too long, and thus were stumbling around and falling over cliffs too much
Recommended textbook explanations
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Earth & Space iScience
The Living Earth Student Edition
Kent Pryor, Lissa Bainbridge-Smith, Richard Allan, Tracey Greenwood
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